In the conventional process called "partial condensation", the hydrogen separated from the gas mixture, after being cooled to a low temperature, is expanded to a pressure of about 5 to 10 bar so as to provide the refrigeration for keeping the plant cold and to cool the gas mixture to below -200.degree. C. A plant of this type is described in U.S. Pat. No. 4,217,759 and uses at least four columns to produce carbon monoxide with a yield of 95% and a purity of approximately 99%. The hydrogen yield is about 99.9%, with a purity of approximately 95%.
The object of the invention is to simplify the process and the plant by reducing the number of columns used for the separation steps, but still maintaining these high purities and yields. Thus, the scrubbing columns usually placed at the head of the process and the distillation column for carbon monoxide/methane separation are eliminated.
The object of the invention is also to ensure that the coldest temperature in the plant is above that of the conventional process, with comparable hydrogen purities and carbon monoxide yields.
DE-A-2,460,515 describes a methane-contaminated hydrogen separation apparatus comprising a first separator, a first stripping column receiving the gas from the first separator, means for sending the head gas into a second separator and means for sending the liquid from the second separator into a second column fed with the liquid from the first separator.
EP-A-0,017,174 describes an apparatus for separating a mixture of carbon monoxide, hydrogen and methane, in which the mixture is partially condensed and the condensed portion is sent into the head of a first stripping column. The head gas from the stripping column is cooled and sent into a second phase separator. The liquid portion is sent into a second column. The base liquid from the second column is fed into the head of a third column and the uncondensed portion from the first phase separator is fed into this base of the third column.
The object of the present invention is also to provide a plant having a lower investment cost than in the prior art, by dispensing with any means of refrigeration.
The invention makes it possible in some cases to achieve complete hydrogen recovery and to obtain the hydrogen at a pressure greater than that obtained in the conventional process.